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- ItemZonalWave Number Diagnosis of RossbyWave-Like Oscillations Using Paired Ground-Based Radars(Hoboken, NJ : Wiley, 2020) He, Maosheng; Yamazaki, Yosuke; Hoffmann, Peter; Hall, Chris M.; Tsutsumi, Masaki; Li, Guozhu; Chau, Jorge LuisFree traveling Rossby wave normal modes (RNMs) are often investigated through large-scale space-time spectral analyses, which therefore is subject to observational availability, especially in the mesosphere. Ground-based mesospheric observations were broadly used to identify RNMs mostly according to the periods of RNMs without resolving their horizontal scales. The current study diagnoses zonal wave numbers of RNM-like oscillations occurring in mesospheric winds observed by two meteor radars at about 79°N. We explore four winters comprising the major stratospheric sudden warming events (SSWs) 2009, 2010, and 2013. Diagnosed are predominant oscillations at the periods of 10 and 16 days lasting mostly for three to five whole cycles. All dominant oscillations are associated with westward zonal wave number m=1, excepting one 16-day oscillation associated with m=2. We discuss the m=1 oscillations as transient RNMs and the m=2 oscillation as a secondary wave of nonlinear interaction between an RNM and a stationary Rossby wave. All the oscillations occur around onsets of the three SSWs, suggesting associations between RNMs and SSWs. For comparison, we also explore the wind collected by a similar network at 54°N during 2012–2016. Explored is a manifestation of 5-day wave, namely, an oscillation at 5–7 days with m=1), around the onset of SSW 2013, supporting the associations between RNMs and SSWs. ©2020. The Authors.
- ItemEvidence for the In‐Situ Generation of Plasma Depletion Structures Over the Transition Region of Geomagnetic Low‐Mid Latitude(Hoboken, NJ : Wiley, 2021) Sivakandan, M.; Mondal, S.; Sarkhel, S.; Chakrabarty, D.; Sunil Krishna, M.V.; Upadhayaya, A.K.; Shinbori, A.; Sori, T.; Kannaujiya, S.; Champati Ray, P.K.On a geomagnetic quiet night of October 29, 2018, we captured an observational evidence of the onset of dark band structures within the field-of-view of an all-sky airglow imager operating at 630.0 nm over a geomagnetic low-mid latitude transition region, Hanle, Leh Ladakh. Simultaneous ionosonde observations over New Delhi shows the occurrence of spread-F in the ionograms. Additionally, virtual and peak height indicate vertical upliftment in the F layer altitude and reduction in the ionospheric peak frequency were also observed when the dark band pass through the ionosonde location. All these results confirmed that the observed depletions are indeed associated with ionospheric F region plasma irregularities. The rate of total electron content index (ROTI) indicates the absence of plasma bubble activities over the equatorial/low latitude region which confirms that the observed event is a mid-latitude plasma depletion. Our calculations reveal that the growth time of the plasma depletion is ∼2 h if one considers only the Perkins instability mechanism. This is not consistent with the present observations as the plasma depletion developed within ∼25 min. By invoking possible Es layer instabilities and associated E-F region coupling, we show that the growth rate increases roughly by an order of magnitude. This strongly suggests that the Cosgrove and Tsunoda mechanism may be simultaneously operational in this case. Furthermore, it is also suggested that reduced F region flux-tube integrated conductivity in the southern part of onset region created conducive background conditions for the growth of the plasma depletion on this night.
- ItemMulti‐Point Measurements of the Plasma Properties Inside an Aurora From the SPIDER Sounding Rocket(Hoboken, NJ : Wiley, 2021) Giono, Gabriel; Ivchenko, Nickolay; Sergienko, Tima; Brändström, UrbanThe Small Payloads for Investigation of Disturbances in Electrojet by Rockets (SPIDER) sounding rocket was launched on February 2nd, 2016 (21:09 UT), deploying 10 free falling units (FFUs) inside a westward traveling auroral surge. Each FFUs deployed spherical electric field and Langmuir probes on wire-booms, providing in situ multi-point recordings of the electric field and plasma properties. The analytical retrieval of the plasma parameters, namely the electron density, electron temperature and plasma potential, from the Langmuir probe measurements was non-trivial due to sheath effects and detailed explanation are discussed in this article. An empirical assumption on the sheath thickness was required, which was confirmed by simulating the plasma environment around the FFU using the Spacecraft Plasma Interaction Software (SPIS). In addition, the retrieved electron density and temperature are also in agreement with the simultaneous incoherent scatter radar measurements from the EISCAT facility. These two independent confirmations provided a good level of confidence in the plasma parameters obtained from the FFUs, and events observed during the flight are discussed in more details. Hints of drift-wave instabilities and increased currents inside a region of enhanced density were observed by the FFUs.
- ItemUsing Principal Component Analysis of Satellite and Ground Magnetic Data to Model the Equatorial Electrojet and Derive Its Tidal Composition(Hoboken, NJ : Wiley, 2022) Soares, Gabriel; Yamazaki, Yosuke; Morschhauser, Achim; Matzka, Jürgen; Pinheiro, Katia J.; Stolle, Claudia; Alken, Patrick; Yoshikawa, Akimasa; Hozumi, Kornyanat; Kulkarni, Atul; Supnithi, PornchaiThe intensity of the equatorial electrojet (EEJ) shows temporal and spatial variability that is not yet fully understood nor accurately modeled. Atmospheric solar tides are among the main drivers of this variability but determining different tidal components and their respective time series is challenging. It requires good temporal and spatial coverage with observations, which, previously could only be achieved by accumulating data over many years. Here, we propose a new technique for modeling the EEJ based on principal component analysis (PCA) of a hybrid ground-satellite geomagnetic data set. The proposed PCA-based model (PCEEJ) represents the observed EEJ better than the climatological EEJM-2 model, especially when there is good local time separation among the satellites involved. The amplitudes of various solar tidal modes are determined from PCEEJ based tidal equation fitting. This allows to evaluate interannual and intraannual changes of solar tidal signatures in the EEJ. On average, the obtained time series of migrating and nonmigrating tides agree with the average climatology available from earlier work. A comparison of tidal signatures in the EEJ with tides derived from neutral atmosphere temperature observations show a remarkable correlation for nonmigrating tides such as DE3, DE2, DE4, and SW4. The results indicate that it is possible to obtain a meaningful EEJ spectrum related to solar tides for a relatively short time interval of 70 days.
- ItemThe Meteoric Ni Layer in the Upper Atmosphere(Hoboken, NJ : Wiley, 2020) Daly, Shane M.; Feng, Wuhu; Mangan, Thomas P.; Gerding, Michael; Plane, John M.C.The first global atmospheric model of Ni (WACCM-Ni) has been developed to understand recent observations of the mesospheric Ni layer by ground-based resonance lidars. The three components of the model are: the Whole Atmospheric Community Climate Model (WACCM6); a meteoric input function derived by coupling an astronomical model of dust sources in the solar system with a chemical meteoric ablation model; and a comprehensive set of neutral, ion-molecule, and photochemical reactions pertinent to the chemistry of Ni in the upper atmosphere. In order to achieve closure on the chemistry, the reaction kinetics of three important reactions were first studied using a fast flow tube with pulsed laser ablation of a Ni target, yielding k(NiO + O) = (4.6 ± 1.4) × 10−11, k(NiO + CO) = (3.0 ± 0.5) × 10−11, and k(NiO2 + O) = (2.5 ± 1.2) × 10−11 cm3 molecule−1 s−1 at 294 K. The photodissociation rate of NiOH was computed to be J(NiOH) = 0.02 s−1. WACCM-Ni simulates satisfactorily the observed neutral Ni layer peak height and width, and Ni+ measurements from rocket-borne mass spectrometry. The Ni layer is predicted to have a similar seasonal and latitudinal variation as the Fe layer, and its unusually broad bottom-side compared with Fe is caused by the relatively fast NiO + CO reaction. The quantum yield for photon emission from the Ni + O3 reaction, observed in the nightglow, is estimated to be between 6% and 40%. ©2020. The Authors.
- ItemOblique Gravity Wave Propagation During Sudden Stratospheric Warmings(Hoboken, NJ : Wiley, 2020) Stephan, C.C.; Schmidt, H.; Zülicke, C.; Matthias, V.Gravity waves (GWs) are important for coupling the mesosphere to the lower atmosphere during sudden stratospheric warmings (SSWs). Here, a minor SSW is internally generated in a simulation with the upper-atmosphere configuration of the ICOsahedral Nonhydrostatic model. At a horizontal resolution of 20 km the simulation uses no GW drag parameterizations but resolves large fractions of the GW spectrum explicitly, including orographic and nonorographic sources. Consistent with previous studies, the simulated zonal-mean stratospheric warming is accompanied by zonal-mean mesospheric cooling. During the course of the SSW the mesospheric GW momentum flux (GWMF) turns from mainly westward to mainly eastward. Waves of large phase speed (40–80 m s -1) dominate the eastward GWMF during the peak phase of the warming. The GWMF is strongest along the polar night jet axis. Parameterizations of GWs usually assume straight upward propagation, but this assumption is often not satisfied. In the case studied here, a substantial amount of the GWMF is significantly displaced horizontally between the source region and the dissipation region, implying that the local impact of GWs on the mesosphere does not need to be above their local transmission through the stratosphere. The simulation produces significant vertically misaligned anomalies between the stratosphere and mesosphere. Observations by the Microwave Limb Sounder confirm the poleward tilt with height of the polar night jet and horizontal displacements between mesospheric cooling and stratospheric warming patterns. Thus, lateral GW propagation may be required to explain the middle-atmosphere temperature evolution in SSW events with significant zonally asymmetric anomalies. ©2019. The Authors.
- ItemRadar Observation of Extreme Vertical Drafts in the Polar Summer Mesosphere(Hoboken, NJ : Wiley, 2021) Chau, J.L.; Marino, R.; Feraco, F.; Urco, J.M.; Baumgarten, G.; Lübken, F.‐J.; Hocking, W.K.; Schult, C.; Renkwitz, T.; Latteck, R.The polar summer mesosphere is the Earth's coldest region, allowing the formation of mesospheric ice clouds. These ice clouds produce strong polar mesospheric summer echoes (PMSE) that are used as tracers of mesospheric dynamics. Here, we report the first observations of extreme vertical drafts (+/-50 ms [hoch]-1) in the mesosphere obtained from PMSE, characterized by velocities more than five standard deviations larger than the observed vertical wind variability. Using aperture synthesis radar imaging, the observed PMSE morphology resembles a solitary wave in a varicose mode, narrow along propagation (3–4 km) and elongated (>10 km) transverse to propagation direction, with a relatively large vertical extent (~13 km). These spatial features are similar to previously observed mesospheric bores, but we observe only one crest with much larger vertical extent and higher vertical velocities.
- ItemMesospheric Q2DW Interactions With Four Migrating Tides at 53°N Latitude: Zonal Wavenumber Identification Through Dual‐Station Approaches(Hoboken, NJ : Wiley, 2021) He, Maosheng; Forbes, Jeffrey M.; Li, Guozhu; Jacobi, Christoph; Hoffmann, PeterMesospheric winds from two longitudinal sectors at 53°N latitude are combined to investigate quasi-two-day waves (Q2DWs) and their nonlinear interactions with tides. In a summer 2019 case study, we diagnose the zonal wavenumber m of spectral peaks at expected frequencies through two dual-station approaches, a phase differencing technique (PDT) on individual spectral peaks and a least squares procedure on family batched peaks. Consistent results from the approaches verify the occurrences of Rossby-gravity modes (m = 3 and 4 at periods T = 2.1 and 1.7 days), and their secondary waves (SWs) generated from interactions with diurnal, semi-diurnal, ter-diurnal, and quatra-diurnal migrating tides. We further extend the PDT to 2012–2019, illustrating that Q2DWs exhibit significant interannual variability. Composite analysis reveals seasonal and altitude variations of the Rossby-gravity modes and their SWs. The Rossby-gravity modes maximize in local summer, whereas their 16- and 9.6-h SWs appear more in winter.
- ItemQuasi‐2‐Day Wave in Low‐Latitude Atmospheric Winds as Viewed From the Ground and Space During January–March, 2020(Hoboken, NJ : Wiley, 2021) He, Maosheng; Chau, Jorge L.; Forbes, Jeffrey M.; Zhang, Xiaoli; Englert, Christoph R.; Harding, Brian J.; Immel, Thomas J.; Lima, Lourivaldo M.; Bhaskar Rao, S. Vijaya; Ratnam, M. Venkat; Li, Guozhu; Harlander, John M.; Marr, Kenneth D.; Makela, Jonathan J.Horizontal winds from four low-latitude (±15°) specular meteor radars (SMRs) and the Michelson Interferometer for Global High-resolution Thermospheric Imaging (MIGHTI) instrument on the ICON satellite, are combined to investigate quasi-2-day waves (Q2DWs) in early 2020. SMRs cover 80–100 km altitude whereas MIGHTI covers 95–300 km. Q2DWs are the largest dynamical feature of the summertime middle atmosphere. At the overlapping altitudes, comparisons between the derived Q2DWs exhibit excellent agreement. The SMR sensor array analyses show that the dominant zonal wavenumbers are s = +2 and + 3, and help resolve ambiguities in MIGHTI results. We present the first Q2DW depiction for s = +2 and s = +3 between 95 and 200 km, and show that their amplitudes are almost invariant between 80 and 100 km. Above 106 km, Q2DW amplitudes and phases present structures that might result from the superposition of Q2DWs and their aliased secondary waves.
- ItemSpring‐Fall Asymmetry in VLF Amplitudes Recorded in the North Atlantic Region: The Fall‐Effect(Hoboken, NJ : Wiley, 2021) Macotela, E.L.; Clilverd, M.; Renkwitz, T.; Chau, J.; Manninen, J.; Banyś, D.A spring-fall asymmetry is observed in daytime amplitude values of very low frequency (VLF) radio wave signals propagating over the North Atlantic during 2011–2019. We explore the processes behind this asymmetry by comparing against mesospheric mean temperatures and the semidiurnal solar tide (S2) in mesospheric winds. The solar radiation influence on VLF subionospheric propagation was removed from the daytime VLF amplitude values, isolating the fall-effect. Similarly, the symmetric background level was removed from mesospheric mean temperatures undertaking comparable analysis. During fall, all three analyzed parameters experience significant deviation from their background levels. The VLF amplitude variation during spring is explained by the seasonal variation in solar illumination conditions, while the fall-effect can be interpreted as a mean zonal wind reversal associated with both a S2 enhancement, and temperature reductions. Decreases in temperature can produce decreases in collision frequency, reducing VLF signal absorption, driving the observed VLF asymmetry.